The present invention relates to a Switchable Liquid-filled Vibration Absorbing Mount to be used for supporting a power unit of an automobile or another vibrating body in a vibration preventing manner.
In the prior art, the liquid-filled vibration absorbing mount has been used as a mount for bearing the vibrating body such as an automotive engine in a manner to transmit of vibration to the vehicular body.
As this liquid-filled vibration absorbing mount, there has been proposed (Japanese Patent Laid-Open or Unexamined Publication Nos. JP-A-1996-270718, JP-A-1998-238586 or JP-A-1998-184777, for example) which is switched for the vibration absorbing characteristics in accordance with two kinds of vibrations of different frequency ranges such as the shaking vibrations or the idle vibrations.
The switchable liquid-filled vibration absorbing mount of the prior art, as disclosed in Unexamined Published Japanese Patent Application No. JP-A-1996-270718, has the following construction, as shown in FIG. 6.
This vibration absorbing device is constructed to comprise: a first rigid mounting fixture (101); a second rigid mounting fixture (102) formed into a bottomed cylindrical shape having a bottom portion positioned at a predetermined distance in the axial direction from the first mounting fixture (101); a vibration absorbing base (103) made of a rubbery elastomer and interposed between the first mounting fixture (101) and the second mounting fixture (102) for jointing the two mounting fixtures (101) and (102); a partition member (104), a first diaphragm (105) and a second diaphragm (106) arranged in series in the axial direction between the vibration absorbing base (103) and the second mounting fixture (102); a main liquid chamber (107) formed between the vibration absorbing base (103) and the partition member (104); an auxiliary liquid chamber (108) formed between the partition member (104) and the first diaphragm (105); an outer orifice (113) and an inner orifice (114) disposed in the partition member (104) for providing a communication between the main liquid chamber (107) and the auxiliary liquid chamber (108), the outer orifice (113) being extended over a predetermined length in the circumferential direction of the partition member (104), the inner orifice (114) being disposed on the inner side of the outer orifice (113) in the diametrical direction and opened/closed by the first diaphragm (105); bias means (127) for pushing the first diaphragm (105) toward the partition member (104) so as to block the flow of the liquid between the inner orifice (114) and the auxiliary liquid chamber (108); a balance chamber (109) formed between the first diaphragm (105) and the second diaphragm (106); and a change-over chamber (110) formed between the second diaphragm (106) and the second mounting fixture (102) and capable of having the atmospheric pressure and a vacuum introduced selectively thereinto. When the vacuum is introduced into the change-over chamber (110), the first diaphragm (105) is moved against the biasing force of the bias means (127) to leave the partition member (104) thereby to provide the communication between the inner orifice (114) and the auxiliary liquid chamber (108). By switching the introductions of the atmospheric pressure and the vacuum into the change-over chamber (110) selectively, the inner orifice (114) can be opened/closed so that the orifices individually coping with the two kinds of vibrations in different frequency ranges can be selectively employed.
In this liquid-filled vibration absorbing mount of the prior art, not only the outer orifice (113) but also the inner orifice (114) to be opened/closed by the first diaphragm (105) is ring-shaped. Therefore, the inner orifice (114) has a certain length to extend in the circumferential direction so that a liquid to flow in the inner orifice (114) is subjected to a flow resistance. As a result, the liquid becomes hard to flow in the inner orifice (114). Thus, the liquid flows in the outer orifice (113) so that a sufficient vibration attenuating effect cannot be obtained in the inner orifice (114).
In order to close the inner orifice (114), on the other hand, the first diaphragm (105) is pushed at its central portion to the lower face of the partition member (104) through a push member (162) by the bias means (127). Specifically, the flat central portion of the first diaphragm (105) comes into abutment against the flat portion of the circumference of an opening (114a) of the inner orifice (114) on the side of the auxiliary liquid chamber (108) in the partition member (104) so that the inner orifice (114) is closed exclusively by such planar abutment. When a high pressure is abruptly built up in the main liquid chamber (107), for example, or when the first diaphragm (105) is transversely displaced or deformed by the rocking motions or the like to slacken the abutting portion slightly, therefore, the inner orifice (114) may not be sufficiently closed so that the stable vibration absorbing characteristics cannot be obtained.
The invention has been conceived in view of the description thus far made and contemplates to improve the aforementioned conventional liquid-filled vibration absorbing mount, in which the inner one of the two inner and outer orifices can be opened/closed to allow the orifices individually coping with the two vibrations of different frequency ranges such as the shaking vibrations and the idle vibrations to be selectively employed, especially the shape of the inner orifice and the shape of the first diaphragm for closing the inner orifice, thereby to solve the aforementioned problems, to exhibit the vibration attenuations effectively in the different frequency ranges and to hold the stable characteristics.
As in the aforementioned liquid-filled vibration absorbing mount, according to the invention, there is provided a switchable liquid-filled vibration absorbing mount comprising: a first mounting fixture; a second mounting fixture formed into a bottomed cylindrical shape; a vibration absorbing base jointing the two mounting fixtures; a partition member, a first diaphragm and a second diaphragm arranged in series between the second mounting fixture and the vibration absorbing base; a main liquid chamber and an auxiliary liquid chamber partitioned by the partition member; two outer and inner orifices and an inner diaphragm disposed for providing a communication between the two chambers; bias means for pushing the first diaphragm toward the partition member; a balance chamber formed between the first diaphragm and the second diaphragm; and a switching chamber formed between the second diaphragm and the second mounting fixture, wherein the improvement resides: in that the inner orifice is an opening extending in the axial direction through the partition member; in that the first diaphragm is provided at its central portion with a valve member for closing the inner orifice, the valve member including: a flat rubber face confronting the lower face of the circumference of the inner orifice in the partition member when the atmospheric pressure is introduced into the change-over chamber, and a protrusion protruding from the flat rubber face and fitted in the inner orifice; and in that by selecting the introduction of either the atmospheric pressure or the vacuum into the switching chamber, the valve member is moved up and down to open/close the opening, and the transverse displacement of the valve member is regulated by the protrusion.
According to this switchable liquid-filled vibration absorbing mount, when the atmospheric pressure is introduced into the switching chamber, the flat rubber face of the valve member belonging to the first diaphragm is biased by the bias means to confront the lower face of the circumference of the inner orifice thereby to hold the inner orifice in the closed state so that the vibration attenuations in the frequency range set for the outer orifice can be effected.
By introducing the vacuum into the switching chamber, moreover, the valve member is caused to leave the partition member (4) against the biasing force of the bias means thereby to open the inner orifice into its active state so that the vibration attenuations in the frequency range set for the inner orifice are effected while suppressing the liquid flow in the outer orifice.
Since the protrusion of the valve member is fitted in the opening, on the other hand, the valve member can be prevented from being transversely displaced or going out of position, and the flat rubber face can confront the lower face of the circumference of the inner orifice of the partition member thereby to prevent the closed state from being slackened, as might otherwise be caused by the displacement of the inner orifice, to retain the sufficient closed state and to warrant the stable characteristics for a long time.
On the other hand, the second diaphragm preferably includes: an annular rubber portion fitted at its outer circumference in the inner circumference of the second mounting fixture; and a pushing auxiliary member jointed to the inner circumferential edge portion of the rubber portion for pushing the flat rubber face from the side of the balance chamber onto the partition member thereby to move the valve member up and down through the pushing auxiliary member. As a result, the valve member can be stablely supported by the second diaphragm through the pushing auxiliary member so that the inner orifice can be satisfactorily opened/closed by the valve member.
The aforementioned liquid-filled vibration absorbing mount is especially preferable to further comprise stopper means for regulating the downward movement of the pushing auxiliary member when the vacuum is introduced into the switching chamber, so that the protrusion of the valve member may not come out of the inner orifice at the time of introducing the vacuum into the switching chamber.
As a result, even when the vacuum is introduced into the switching chamber to open the inner orifice, the protrusion is held in the inner orifice, and the valve member can be positioned to confront the inner orifice without being transversely displaced or going out of position, so that the opening/closing actions can be performed satisfactorily stablely at all times.
The stopper means preferably includes a stopper portion made of rubber integrally with the rubber portion and disposed at the lower end portion of the pushing auxiliary member of the second diaphragm, so that the stopper portion may come into abutment against the bottom portion of the second mounting fixture at the time of introducing the vacuum into the switching chamber, thereby to regulate the downward movement of the pushing auxiliary member. As a result, the aforementioned stopper action is performed reliably and satisfactorily.
The second diaphragm is preferred to have its rubber portion vulcanized and shaped so that it may take a shape between the shape at the time of introducing the atmospheric pressure into the switching chamber and the shape at the vacuum introducing time. As a result, the change in the shape of the rubber portion, as caused by switching the opening/closing actions of the inner orifice can be minimized to improve the durability of the rubber portion.
The protrusion of the valve member is preferably tapered to converge and to have a root diameter substantially equal to or slightly smaller than the internal diameter of the inner orifice. With this shape, more specifically, the protrusion performs a guide action while the valve member is moving upward to close, even if it grows slightly eccentric to or inclined from the inner orifice being opened. Thus, the valve member can confront the partition member at a position substantially coaxial with the inner orifice, thereby to close the inner orifice reliably.
The second mounting fixture can include: a cylindrical fixture vulcanized and adhered at its upper portion to the vibration absorbing base; and a bottom cylinder fixture having a bottom portion and caulked and fixed to the lower end portion of the cylindrical fixture. The second diaphragm is attached by press-fitting the outer circumference of the rubber portion including a reinforcing ring-shaped fixture in the cylindrical portion of the bottom cylinder member. Moreover, the partition member and the first diaphragm are individually caulked and fixed at their outer circumferential edge portions to the caulked and fixed portions between the cylindrical fixture and the bottom cylinder fixture.
As a result, it is possible to provide a product which can be easily assembled and which can retain a high reliability even for the loading liquid pressure after mounted.
The switchable liquid-filled vibration absorbing mount can further comprise a boss fixture mounted in the bottom portion of the second mounting fixture and having a vacuum and atmospheric pressure introducing tube extending therethrough. The bias means is interposed between the boss fixture and the pushing auxiliary member and positioned by the boss fixture. As a result, the bias means can be stablely held.